2021082a0Nature202493719640613108210830028-0836196410.1038/2021082a0ukNatureNatureNATUREnatureNature is a weekly international journal publishing the finest peer-reviewed research in all fields of science and technology on the basis of its originality, importance, interdisciplinary interest, timeliness, accessibility, elegance and surprising conclusions. Nature also provides rapid, authoritative, insightful and arresting news and interpretation of topical and coming trends affecting science, scientists and the wider public./nature/journal/v202/n4937issueJournal homeArchiveCurrent issueAdvance online publicationPrivacy policySubscribeNature Publishing GroupCurrent issue2021082a0Preservation of Viability in the Isolated Monkey Brain Utilizing a Mechanical Extracorporeal Circulation
AU  - WHITE, ROBERT J.
AU  - ALBIN, MAURICE S.
AU  - VERDURA, JAVIERSection of Neurosurgery, Cleveland Metropolitan General Hospital and Western Reserve University School of Medicine, Cleveland, OhioIN a recent communication we described our experience in surgically preparing and viably sustaining the monkey brain as an isolated organ via extracorporeal donor perfusion. By substituting a completely mechanical extracorporeal system incorporating a small disk oxygen-ator for the donor monkey, significant electrocortical activity, A-VQ% and F-^4cot differences, and glucose utilization were measured in the isolated monkey brain.
The operative preparation and anaesthetic management of the isolated brain differed in no way from that previously described1. In essence, the brain was surgically freed from all contiguous tissue except a small basal plate of bone and a thin bony strip over the sagittal sinus which provided anatomical support for the brain and the electrode recording system. Vascular isolation was achieved by removal of all extracranial vasculature and ligation of the vertebral arteries after the carotid arteries were cannulated with metal T cannulse permitting autogenous cerebral perfusion until extracorporeal circulation was begun. Neurogenic isolation was accomplished with ligation and division of the spinal cord at Ci-C2. Extracorporeal perfusion was commenced as the brain was separated from the body by severing the spinal column at this same level and after the carotid arteries were occluded and divided behind the T cannulse.
The extracorporeal circulatory system (Fig. 1) consisted of a heated 70-ml. aluminium reservoir positioned beneath the venous outflow of the brain and connected via 'Tygon' tubing and a small occlusive venous pump to a miniature disk oxygenator2. The total priming volume of this oxygenator was less than 90 ml. when a specially designed Gebauer heat exchanger was placed in its reservoir. The oxygenator was directly connected via a small arterial pump and a Y 'Tygon' tube to the two metal T cannulae surgically secured in the carotid arteries. The extracorporeal system was filled (150 ml. total volume) with freshly drawn, heparinized, compatible monkey blood diluted one third with dextran. The blood was circulated through the oxygenator prior to final connexion to the isolated brain to assure adequate oxygenation. Due to the incorporation of heating units and thermistors in the blood reservoirs, the temperature of the brain could be adjusted over a selected thermal range by the simple expediency of altering the temperature of the perfusing blood. For these experiments intracerebral temperatures were maintained between 28 and 32 C for the purpose of reducing brain metabolism.
Fig. 1. The isolated monkey brain during extracorporeal perfusion. (1) Cerebellum; (2) parietal lobe; (3) a strip of skull containing electrodes; (4) cortical electrodes; (5) frontal lobe; (6) temporal lobe; (7) fixation unit; (8) EEG plug-in box; (9) electrode cable to EEG preamplifiers; (10) venous reservoir thermistor; (11) arterial line; (12) 'wire stirrups'to support arterial cannulse; (13) internal carotid arteries; (14) carotid arteries containing metal T cannulae; (15) collecting funnel for venous reservoir; (16) venous reservoir; (17) heating unit for reservoir; (18) venous line; (19) occlusive arterial pump; (20) occlusive venous pump; (21) disk oxygenator; (22) water line for heat exchanger; (23) oxygen inlet; (24) arterial pressure line; (25) pressure transducer; (26) cable connexion to oscillographic recorder; (27) EEG leads from isolated brain
Fig. 2. Lateral view of the isolated monkey brain placed in its suspension-recording unit. Note the Y arterial line connected to the carotid T cannulse and the venous reservoir directly beneath the brain. The oxygenator is behind the reservoir, the arterial and venous pumps are shown at the inferior corners of the photograph. The needle thermistors are located in the venous reservoir and oxygenator
Utilizing cerebral blood flows of 30-67 ml./min, seven isolated monkey brains were maintained as functioning organs for 2-7 h (Fig. 2). Inspection of the brain surface during the early phase (first 2 h) of perfusion revealed obvious colour differences between cortical arteries and veins, and a normal appearing cortex. During this period, and at reduced cerebral temperatures, significant electrical activity (Fig. 3) was monitored from three pairs of silver disk electrodes placed on the cortical surface and connected to a four-channel Grass polygraph with electro-encephalographic preamplifiers. In the majority of the experiments, the brain began to swell after 3 h of artificial circulation. This observable change in brain bulk was associated with a measurable reduction in electrocortical activity (Fig. 3) and a marked increase in brain-weight (average brain-weight 93 g) post-perfusion. The introduction of 'Metrazol' into the circulating blood resulted in a convulsive discharge of the isolated brain (Fig. 4) even after the above evidences of biological decay were present. Further documentation of the progressive increase in brain volume and reflecting a rising cerebro -vascular resistance was the inevitable increase in perfusion pressure from initial values of 120 mm mercury to more than 250 mm mercury as measured in the carotid cannula via a catheter and pressure transducer connected to an oscillographic recorder.
In spite of reduction in brain temperature, significant roea,n A-VQ^ and V-Aco[ast] differences across the isolated monkey brain, respectively 2-8 vol. per cent and 2-4 vol. per cent, were measured. These values, while low, compare favourably with similar measurements made at 29 C in the monkey brain in situ[ast].
Fig. 3. Interval samplings of electrocortical activity from the frontal and parietal lobes of the isolated monkey brain supported solely by a mechanical extracorporeal circulation system (intracerebral temperature 30-32 C). Observe the gradual decline of electrocortical activity after 3-5 h of continuous pump-oxygenator perfusion which contrasts markedly with that of earlier recordings
Fig. 4. Bipolar tempDral lobe. 'Metrazol' seizure patterns 6 h on perfusion
Minimal support of metabolic activity in the isolated brain was provided by the addition of 150 mg of glucose each hour during extracorporeal perfusion. In two experiments, uptake of glucose in closed mechanical circuit after 2 h of perfusion measured 120 and 126 mg per cent per h. While liver tissue extracts and amino-acids, which have been reported4 as necessary for cerebral function, were not introduced into the isolated circulation, the eventual development of cerebral oedema and biological decay in the isolated brain was also associated with the non-removal of the breakdown products of cerebral metabolism and the mechanical destruction of the perfusing blood. With the passage of time, high levels of lactate (75-5 mg per cent after 2 h) and pyruvate (8-4 mg per cent after 2 h) associated with a gradually developing acidosis (pH 7-2 after 3 h) were continuously being delivered to the isolated organ as part of its extra-corporeal circulating fluid. Significant elevations in free hsemoglobin (up to 4-9 mg per cent) were also measured in the perfusion media after 3 h of uninterrupted circulation. 
In spite of the self-limiting design of these experiments and the eventual development of reduced biological function, this investigation demonstrates for the first time the feasibility of protracted survival of the sub-human primate brain as a totally isolated organ, solely supported by a mechanical circulation system.
We thank Dr. Leo Massopust, neurophysiologist, and Mr. Ron Meder, electronics engineer, of the Cleveland Psychiatric Institute, Cleveland, Ohio, for their assistance.
This work was supported by a U.S. Public Health Service research grant (NB 03859-02 from the National Institute of Neurological Diseases and Blindness).White, , R., Albin, , A., and Verdura, , J., Science, 141, 1060 (1963).PubMedISIChemPortMeder, , R., Massopust, , L., White, , R., Verdura, , J., and Albin, , M., Proc. Eng. Med. Bio., 5, 28 (1963).Bering, , E., Tareu, , J., McMurrey, , J., and Bernhard, , W., Surg. Gyn. Obst., 102, 134 (1956).PubMedISIGeiger, , A., Neurochemistry, second ed., edit. by Elliott, K. A. C., Page, I., and Quastel, J. H., 130 (Charles C. Thomas, Springfield, Ill., 1962).